pseudomorphid

Pseudomorphid is a term used in mineralogy to describe a mineral that has taken on the external form of another mineral. This occurs when a mineral undergoes a chemical change or replacement process, such as dissolution and subsequent recrystallization, while retaining the crystal shape of the original mineral. The resulting mineral is called a pseudomorph, and the original mineral's form is referred to as the morph. For instance, goethite can form pseudomorphs after pyrite, meaning the goethite crystals will exhibit the cubic or pyritohedral shapes characteristic of pyrite. Similarly, quartz can pseudomorph after calcite, inheriting the rhombohedral habit of the original calcite. The process of pseudomorphism can be quite complex, involving various chemical reactions and transport of ions. Identifying pseudomorphs often requires careful observation of the crystal shape, along with mineralogical tests to determine the actual chemical composition and internal structure of the mineral. These occurrences can provide valuable insights into the geological history and alteration processes of a mineral deposit.